Infertiliy is a public health issue that 10-15% of couples suffer from. In 30% of the cases the causative factor is male. There are numerous etiologies of male infertility and oxidative stress plays a role in a lot of them. Oxidative stress is a state in which the oxido-reductive homeostasis is impaired and that leads to production of reactive oxygen species (ROS), reactive molecules that contain an unpaired electron. ROS have a tendency towards stability and react with the surrounding molecules while damaging them. A surprising amount of ROS are produced in the spermatozoa. This is because ROS have a few physiological roles. They play an important role in sperm capacitation, hyperactivation and fusion of the sperm with the oocite. A large portion of ROS is produced as a byproduct of aerobic metabolism, and some come from peroxidase-positive leukocytes. Harmful effects of oxidative stress on spermatozoa include lipid peroxidation, DNA fragmentation and apoptosis. Varicocele is one of the most prevalent etiology of male infertility and it has been linked with oxidative stress due to temperature, hypoxia and inflammation. A link between oxidative stress and infertility has been found in various diseases and conditions such as infection, diabetes, alcoholism and obesity. Lifestyle factors such as smoking and environmental factors such as radiation and exposure to phthalates found in plastic are also linked to oxidative stress. Oxidative stress can also occur iatrogenically, during the use of assisted reproductive technologies and cryopreservation of sperm. Malignancy treatment in form of chemotherapy and radiotherapy can lead to oxidative stress and infertility. First line of defense against oxidative stress are antioxidants that neutralise ROS. There are enzymatic and non-enzymatic antioxidants. Enzymatic are superoxide dismutase, catalase and glutathione peroxidase and they are present in sperm cells and seminal fluid. Non-enzymatic can be obtained from food, some of which are vitamin E, vitamin C, zinc and selenium. Antioxidant deficiency due to poor diet can also lead to oxidative stress and infertility which is why a healthy and balanced diet is a great factor in fertility.